1. Field of the Invention
The present invention relates to a method of controlling an electric motor while adjusting at least one control parameter under each one of a plurality of operating conditions; a motor controlling apparatus for controlling an electric motor in this method; and a recording apparatus that includes a recording head, a carriage on which the recording head is mounted, and this motor controlling apparatus used to move the carriage.
2. Discussion of Related Art
There has conventionally been known a controlling system including a controller that obtains, using at least one control parameter, operating amounts each to be applied to an electric motor so as to operate it and thereby drive an object. In addition, there has conventionally been known a controlling method in which at least one control parameter used by a controller to obtain operating amounts is not fixed but is changed as time elapses while an electric motor is operated at each of the obtained operating amounts so as to drive an object.
More specifically described, while the object is driven by the electric motor, the control parameter is adjusted, at each of appropriate timings, such that a driven amount of the object accurately follows a target driven-amount trajectory, for example, once the driven amount of the object deviates from the target trajectory, the deviation eventually disappears. This adjustment of the control parameter can be done using a well-known adaptive control method.
FIGS. 15, 16A, and 16B show an example in which as at least one control parameter is adjusted, an actual driven amount of an object eventually coincides with a target driven-amount trajectory. FIG. 15 is a graph representing a time-wise change of an actual velocity of an object (e.g., a carriage of an image recording apparatus) when an object is iteratively driven or moved at regular intervals of time in one direction, and a corresponding target velocity trajectory. FIG. 16A is an enlarged view of a first portion of the graph of FIG. 15 that corresponds to a time period from 0.4 second to about 2.0 seconds; and FIG. 16B is an enlarged view of a second portion of the graph of FIG. 15 that corresponds to a time period from 22.4 seconds to about 24 seconds.
As shown in FIGS. 15 and 16A, since when the movement of the object begins, the adjustment of the control parameter begins, the actual velocity of the object largely deviates, at the beginning, from the target velocity trajectory. However, as time elapses, the control parameter is iteratively adjusted to converge to an appropriate value, i.e., a convergent value corresponding to an actual operating condition (i.e., a dynamic characteristic) of the image recording apparatus. Thus, as shown in FIGS. 15 and 16B, eventually, the actual velocity of the object substantially follows the target velocity trajectory. The convergent value of the control parameter reflects the actual operating condition (the dynamic characteristic) of the image recording apparatus at that time. Therefore, so long as the dynamic characteristic does not change, the object can be driven, using the adjusted control parameter (i.e., the convergent value thereof), to follow the target velocity trajectory.
Meanwhile, there is such a case where an object is driven under each one of a plurality of driving conditions corresponding to different dynamic characteristics. Even if at least one control parameter may be adjusted while the object is driven under each one of the driving conditions, the control parameter does not converge to an appropriate value. An example of this case occurs to a carriage driving system in which a carriage (i.e., an object) carrying a recording head to eject ink toward a recording medium (e.g., a recording sheet) is connected to a portion of an endless belt wound on two pulleys, and one (i.e., a drive pulley) of the two pulleys is rotated by an electric motor, to drive or move linearly the carriage between the two pulleys.
In the above-indicated carriage driving system, when the electric motor is rotated in one direction (i.e., a forward direction), the carriage is moved from the drive pulley toward the other (driven) pulley; and when the motor is rotated in the opposite direction (i.e., a backward direction), the carriage is moved from the follower pulley toward the drive pulley. Thus, the carriage is reciprocated between the two pulleys.
In the carriage driving system constructed as described above, when a controller controls or operates the motor to drive or move the carriage as the object, the carriage (or the carriage driving system) exhibits different dynamic characteristics that correspond to (a) a first driving condition that the carriage is moved in one direction corresponding to the forward rotation direction of the motor and (b) a second driving condition that the carriage is moved in the opposite direction corresponding to the backward rotation direction of the motor. The different dynamic characteristics of the carriage can be said as different dynamic characteristics of an object(s) controlled by the controller, i.e., a combination of the motor and the carriage. Thus, when the single motor as a drive source of the carriage driving system is rotated in the different directions, the motor appears, to the controller, to behave as if the motor drove different carriages, that is, the combination of the motor and the carriage appears, to the controller, to behave as if the controller controlled different combinations of motors and carriages.
In order that the carriage having the different dynamic characteristics corresponding to the different movement directions may be so driven or moved as to follow the target velocity trajectory, the control parameter is adjusted while the carriage is moved. More specifically described, when the carriage is moved in one direction, the control parameter is adjusted to converge to a first convergent value suitable for the dynamic characteristic corresponding to the one direction; and when the carriage is moved in the opposite direction, the control parameter is adjusted to converge to a second convergent value suitable for the dynamic characteristic corresponding to the opposite direction. Since the first and second convergent values differ from each other, the control parameter is oscillated between the two convergent values as the carriage is iteratively reciprocated between the two pulleys.
That is, each time the carriage changes its movement directions, it also changes its dynamic characteristics. Therefore, the control parameter converges alternately to the two convergent values, and does not converge to a single convergent value even in a long time duration. That is, the control parameter continues to change or oscillate between the two convergent values. If the control parameter does not converge to a single convergent value even in a long time duration, the time-wise change of the actual velocity of the carriage does not coincide with the target velocity trajectory, as shown in FIGS. 17, 18A, and 18B. Thus, the carriage cannot be driven in an appropriate manner and accordingly the recording head mounted on the carriage cannot record an excellent image on the recording medium.
FIG. 17 is a graph representing a time-wise change of an actual velocity of an object (e.g., a carriage) when the object is iteratively driven or moved at regular intervals of time in each of opposite directions, and a corresponding target velocity trajectory. FIG. 18A is an enlarged view of a first portion of the graph of FIG. 17 that corresponds to a time period from 0.4 second to about 2.0 seconds; and FIG. 18B is an enlarged view of a second portion of the graph of FIG. 17 that corresponds to a time period from 22.4 seconds to about 24 seconds. As shown in those figures, each time the object changes its movement directions, it also changes its dynamic characteristics, so that a control parameter does not converge to a single convergent value. That is, the control parameter does not converge to any appropriate values corresponding to the different movement directions, so that the time-wise change of the actual velocity of the carriage does not coincide with the target velocity trajectory even in a long time duration.
In the above-described carriage driving apparatus as an operating apparatus, the carriage (or the carriage driving apparatus as a whole) changes its dynamic characteristics not only when the carriage is moved in the different directions but also because of secular variation. For example, Japanese Patent Application Publication No. 7(1995)-210216 discloses a moving apparatus that may be used as a recording-head moving apparatus of a printer and that changes its characteristic (i.e., its transfer function) because of secular variation. In order to prevent the moving apparatus from becoming unable to stop an object at a target position after accelerating or decelerating it, a control parameter is adaptively changed.
The adaptive changing of the control parameter is carried out as follows: A disconnecting device is employed that can disconnect a drive pulley and an endless belt of the moving apparatus from each other. First, using the disconnecting device, the endless belt is disconnected from the drive pulley, and a rotary portion of the moving apparatus is identified. Next, in a state in which the endless belt is connected to the drive pulley, the moving apparatus is identified by utilizing the result obtained by the identification of the rotary portion. Then, based on the respective results obtained by the identification of the rotary portion and the identification of the moving apparatus, an optimum waveform (i.e., an operating amount) to be inputted to the of the moving apparatus is obtained. This changing of the control parameter is carried out at a predetermined period, or as needed. Thus, even if the characteristic of the moving apparatus may change because of secular variation, the printer can maintain its excellent recording quality.